The present work deals with the modification of casting solutions for polysulfone gas separation membranes fabricated by wet-phase inversion. The aim was to fabricate membranes with thin gas separation layers below one micrometer of thickness and a sponge-like support structure. With decreasing thicknesses of the separation layers, increasing permselectivities were observed. For the first time, we could show that permeabilities and diffusion coefficients of certain gases are orders of magnitude lower in separation layers of membranes below 500 Å of thickness compared to separation layers with a thickness above 1 micrometer. These results indicate that the selection of the solvent system has a huge impact on the membrane properties and that the permeability and diffusion coefficient are not material-related properties. Thus, they cannot be applied as specific indicators for gas-separating polymers. In this publication, scanning electron microscopy and gas permeation measurements were carried out to prove the gas separation properties and morphologies of polysulfone membranes.

Biopolymers arise as environmentally benign alternatives to bio-accumulating, fossil resource-based synthetic polymers for a variety of applications, many of which require self-standing films or membranes. Novel sustainable amine-functionalized cellulose nanocrystals (CNCs) form dense films with low porosity suitable for gas barriers. Due to their brittleness, pure CNC membranes are challenging to work with but represent an attractive support material for selectivity-inducing additives. Supported ionic liquid membranes (SILMs) are promising due to their tunable properties and good performance in gas separation. In this study, we investigate the possibilities to realize such applications by applying glucose and ionic liquids (ILs) as additives with different functions in CNC-based membranes. By the choice of the plasticizer, the gas permeation behavior of the flexible self-standing films can be tuned from impermeable, using glucose as an additive, to permeable by addition of the ILs 1,3-dibutylimidazolium acetate and 1,3-ditetrahydrofurfurylimidazolium acetate. Tunability is also observed through the choice of the CNC source in the form of an inversed selectivity of the gas pair N2/O2, which was traceable to the CNCs’ source-specific properties. The contributions of the matrix and additive were analyzed by comparing CNC to chitosan membranes and considering gas solubilities and diffusivities. The obtained results underline the diversity and tunability of bio-derived functional materials.

Supporting Information available onlinePolysulfon (PSU) ist ein geeignetes Material fu ¨r die industrielle Gastrennung. In der vorliegenden Studie konnten mit speziellen Gießlo ¨sungen u ¨ber den Trocken/Nass-Phaseninversionsprozess PSU-Flachmembranen mit einer poro ¨sen Stu ¨tzstruktur und einer trennaktiven Deckschicht im Mikrometerbereich in einem Schritt hergestellt werden. Durch Variation der Zusammensetzung der Gießlo ¨sung und des Fa ¨llungsmediums konnte die Auspra ¨gung der einzelnen PSU-Schichten variiert werden. Zum Nachweis der Schichtstrukturen der PSU-Flachmembranen wurden rasterelektronenmikroskopische Aufnahmen angefertigt. Die Gastrenneigenschaften wurden anhand von Permeabilita ¨ten und idealen Trennfaktoren durch Gaspermeationsmessungen ermittelt.